An inkjet recording method has become rapidly popular in these days because it can record color images on plain paper and its running cost is low. However, the inkjet recording method has problems that image defects typified by character feathering (hereinafter, referred to as feathering) easily occur depending on the combination of an ink with a recording medium used, causing significant degradation in image quality. Thus, an attempt has been made such that ink permeability is suppressed so as to prevent feathering. However, in this case, since the drying properties of an ink degrade, hands are stained by the ink of a recorded matter and an image smear occurs.
When a color image is recorded by the inkjet recording method, different color inks are sequentially superimposed one another. As a result, color inks bleed and are mixed together at the boundary parts of colors (hereinafter, referred to as color bleeding), and image quality significantly degrades. To solve these problems, attempts have been made to prevent the color bleeding by increasing ink permeability. However, in this case, since a colorant penetrates inside the recording medium, image density degrades, and ink significantly strikes through to the back surface of the recording medium, failing to perform double face printing in a suitable manner.
To solve these problems and improve image quality, image forming methods using a treatment liquid and an ink have been proposed. However, improvement in image quality using the treatment liquid causes decrease in the drying properties of an image and increase in smear. Unevenness of image improvement effect causes uneven density of an image.
In order to uniformly apply a treatment liquid to a recording medium, the following methods have been considered: a method of ejecting a treatment liquid from a head so as to apply the treatment liquid to a recording medium (see PTL 1); a method of atomizing a treatment liquid by air pressure (see PTL 2); and a method of uniformly applying a treatment liquid to a recording medium by controlling a pressure of a coating roller and an opposing roller (see PTL 3).
However, in the method of ejecting a treatment liquid from a head so as to apply the treatment liquid to a recording medium, in order to stably jet the treatment liquid, the viscosity and surface tension of the liquid are restricted. Additionally, the diameter of a nozzle and a liquid composition are restricted so as not to clog the nozzle, causing significant decrease in flexibility. Since in the case where the small amount of the treatment liquid is applied to a recording medium, in an area to which liquid droplets adhere spaces are formed between the adhered liquid droplets, causing nonuniform coating, it is necessary to increase the amount of the treatment liquid to be applied. However, in the case where the amount of the treatment liquid to be applied is increased, the drying properties degrades. In the method of atomizing a treatment liquid by air pressure, it is necessary to provide a space for atomization, and an apparatus cannot be downsized. Moreover, since the amount of the treatment liquid which is not applied to a medium is larger than the amount of the treatment liquid applied to the medium, there are problems on cost and environment. In the method of uniformly applying a treatment liquid to a recording medium by controlling a pressure of a coating roller and an opposing roller, it is impossible to completely prevent uneven coating using some types of the treatment liquids. It is necessary to improve the treatment liquid. For example, by incorporating a fluorochemical surfactant and a cationic compound into the treatment liquid, a method of satisfying both improvement in image quality and improvement in fixability (PTL 4) has been proposed. The improvement in image quality and improvement in fixability are achieved, but the treatment liquid foams upon coating, causing uneven coating and failing to obtain image uniformity.